Protecting the skin from pollution

Move over UV and sunscreen, the next big thing in anti-ageing is pollution and pollution prevention. Many types of pollution are well known to be harmful when inhaled, but there hasn’t been much information about how they interact with skin until quite recently. A handful of newer studies have shown that pollution is linked to skin allergies, ageing and slower recovery from damage.

So how does pollution affect your skin?
Different types of pollution cause different varieties of skin damage, but the two most important ones are:

1. Oxidative stress: Pollution causes the production of highly reactive free radicals, which cause all sorts of non-specific damage to the biological structures in your skin. They’re like hyperactive bulls in a china shop. The increase in free radicals leads to the activation of matrix metalloproteinase enzymes which break down collagen in the skin. It also sets off inflammatory cascades that can slow down collagen formation and decrease the amount of fat underlying the skin, causing wrinkling. Check out this article for more on oxidative stress and antioxidants.
2. Activation of arylhydrocarbon receptors (AhR): Activation of AhRs on skin cells is linked to inflammation and pigmentation. There’s also evidence that it causes the activation of MMP-1, a matrix metalloproteinase.

There are different types of pollution which must be factored in and those of most relevance to skin ageing are:

1. particulate matter
2. ozone
3. nitrogen dioxide 

Particulate Matter
The particulate matter (PM) that’s relevant in skin health is small pieces of soot, and is usually produced from combustion of fossil fuels such as the burning of petrol in car engines. Technically though, any small solid particles are included in particulate matter.

Particulate matter is usually classified according to the size of the particles. PM10 includes coarser particles 2.5 to 10 microns in diameter and come from dust and industrial emissions, while smaller PM2.5 particles are less than 2.5 microns across and usually come from fires, power plants and motor vehicle exhaust. (For reference, the thinnest human hair is about 17 microns across.)

Because of their large surface area, particulate matter is good at reacting with skin and causing oxidative stress. Because of their small size, they can penetrate into cells and produce oxidative stress in mitochrondria. One of the other concerns about particulate matter is that other pollutants, like polyaromatic hydrocarbons (PAHs), can latch onto them, which means they’re a very efficient means of delivering large amounts of pollutants to your skin. PAHs can activate the AhR pathway, so particulate matter can age skin in that way as well.

In a few studies, exposure to particulate matter was linked to formation of wrinkles and pigment spots – in one study, increased exposure to particulate pollution was correlated to a 20% increase in pigmented spots on the cheeks and forehead. There’s also evidence that particulate pollution can exacerbate atopic dermatitis, psoriasis, acne and skin cancers.

Ozone (O3)
Ozone is an oxidant that’s produced when other pollutants (primarily from cars) react in sunlight, in a phenomenon known as photochemical smog. It’s particularly bad around high-traffic areas in summer, and can cause asthma attacks. When ozone interacts with skin, it depletes its natural antioxidant stores (particularly vitamins E and C), which leaves it more susceptible to free radical damage and oxidative stress. It also damages proteins and lipids in your skin.

Ozone exposure has been linked to increased MMP-9, a collagen-degrading enzyme, in animal studies. Ozone can also activate AhR in skin, which could lead to inflammation and pigmentation.

Nitrogen Dioxide (NO2)
Nitrogen dioxide is a brown, acrid-smelling gas produced by motor vehicles and power plants. There hasn’t been as much research performed on NO2's impact on the skin, but it’s been correlated with increased pigment spots.

HOW TO PROTECT YOUR SKIN FROM POLLUTION
What can you do to protect your skin from pollution, aside from run away to a mountaintop and live as a hermit for the rest of your life? Luckily a lot of products you already own will probably protect your skin from pollution, although you’ll see their anti-pollution benefits emphasised more and more.

Antioxidants 
One way to protect your skin against oxidative stress is to apply antioxidant products. Antioxidants like vitamin C, N-acetylcysteine and green tea polyphenols can decrease the response to ozone in vitro, and a very recent study found that vitamin C serums reduced some of the ageing responses to ozone in human forearm skin.

Barrier Protection 
Many trending skincare ingredients are designed to form a shield between your skin and pollutants. There seems to be a lot of variety with the ingredients that can potentially do this, which is unsurprising, since a lot of ingredients can form sticky gooey films on your skin. Since pollution protection is so new, none of these have peer-reviewed studies to support them yet as far as I know, but some are supported by manufacturer studies. 

Regular and Effective Cleansing Routine
You’ll want to thoroughly clean any accumulated pollution off your skin at the end of the day, but if you clean too thoroughly, you risk impairing your skin’s protective ability. Check out next month's blog post on the verdict on soap & water versus cleanser & toner. 

AHR Antagonists
An interesting new way of protecting against pollution damage is by using molecules that can block AhR activation. A formula containing 0.5% of an AhR antagonist BDDI was found to reduce activation of genes related to ageing in a clinical study.

Conclusions
UV is still the number 1 environmental cause of ageing, so if you haven’t sorted out your sun protection, I wouldn’t even bother thinking about pollution. But if you’re protecting yourself from UV and you want more, and you’re exposed to high pollution urban environments, then anti-pollution is a good place to look next!

FURTHER READING

1. SE Mancebo & SQ Wang, Recognizing the impact of ambient air pollution on skin health, J Eur Acad Dermatol Venereol 2015, 29, 2326-2332.
2. A Vierkötter, T Schikowski, U Ranft, D Sugiri, M Matsui, U Krämer & J Krutmann, Airborne particle exposure and extrinsic skin aging (open access), J Invest Dermatol 2010, 130, 2719-2726.
3. A Vierkötter & J Krutmann, Environmental influences on skin aging and ethnic-specific manifestations (open access), Dermatoendocrinol 2012, 4, 227-231.